Interstate Aircraft and Engineering Corporation entered the aircraft manufacturing field in 1940 with the S-1 Cadet, a tandem seat monoplane. Specifically designed for the Civilian Pilot Training Program, its paramount features were tough construction and economical operation with minimum maintenance. A later prototype design, based on series production of S-1A models, was delivered to the U.S. Army Air Forces (AAF) as the XO-63—it has the distinction of being the last airplane to use the “O” designation. When the United States entered World War II, the AAF contracted with Interstate for 250 of its now S-1B1 variant and designated them L-6 for military service.

While the L-6 was said to be faster, stronger, and more suitable to a rugged environment than comparable “liaison” aircraft, the Interstate L-6 cost almost three times as much. Recurrent engine troubles hampered its use by the AAF, thus the Interstate had the unfortunate distinction that fewer were built (a total of 259) than any other AAF liaison aircraft. Seeing service primarily in the United States, the L-6 was used for transport, liaison exercise, and flight training. Interstate was based in El Segundo, California.


Wingspan: 35 ft 6 in
Length: 23 ft 5 in
Height: 7 ft 3 in
Empty weight: 1,103 lb
Max. takeoff weight: 1,650 lb
Wing area: 173.8 sf
Armament: None
Engine: Franklin 4ACG-199-H3, 113 hp (S-1B1 / Army L-6)
Crew: Two (pilot and passenger)
Cost: $6,000


Max. speed: 117 mph / 102 kt
Cruise speed: 105 mph / 91 kt
Rate of climb: 800–1,000 fpm
Range: 540 miles
Service ceiling: 16,500 ft
Wing loading: 7.45 lb/sf

The Interstate S-1A at Cannon Field makes a Fall foray.
Interstate S-1A operating out of Cannon Field.
Interstate S-1A at Cannon Field, May 1982.
Interstate S-1A Cadet over Karnes City, Texas.

Your tax deductible donation will help to support the preservation of this aircraft.

If you prefer to give by mail, send your check payable to: Alamo Liaison Squadron, 2352 S. Loop 1604 W., San Antonio, Texas 78264. Please write “Donation” in the memo line.

L-6 (Interstate S-1B1) formerly based at Cannon Field, 1986.

Notes: Eight examples of the Interstate S-1A Cadet were ordered for the Bolivian Air Force and designated as L-8A. Distinguishing features of the L-6 include: enlarged cabin with “greenhouse” windows, balanced horizontal stabilizer with elevator horn, cabin door swings up (on the L-8/Cadet it swings forward).

For more info on the L-6/L-8 check out this article by Matthew McDaniel.